DEMO MANUAL DC2311A
LTC3370EUH
4-Channel 8A Configurable
Buck DC/DCs
Description
Demonstration circuit 2311A is a 4-output power supply
featuring the
LTC
®
3370.
The LTC3370 has four current
mode synchronous buck regulators which can be config-
ured to share eight individual 1A power stages to create
one of eight combinations of 1A, 2A, 3A and 4A regulators.
The DC2311A is set up as four 2A buck regulators but
can be modified to one of the other seven configurations.
The input range of the LTC3370 is ideal for single cell
Li-Ion/Polymer battery applications. The buck regulators
are enabled via external precision threshold enable pins
to allow hardwired power up sequences.
The LTC3370 has a default operating frequency of 2MHz
but can be set between 1MHz to 3MHz using an external
resistor. The LTC3370 also has a PLL/MODE pin which
allows the internal oscillator to synchronize to an external
clock from 1MHz to 3MHz or configure the regulators to
forced continuous mode or burst mode.
Refer to the LTC3370 data sheet for more details on the
electrical and timing specifications.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2311A.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
performance summary
Input Supply Range (VINA-H)
VCC Operating Voltage
V
OUT1
V
OUT2
V
OUT3
V
OUT4
Specifications are at T
A
= 25°C
2.25
2.7
0 to 2A
0 to 2A, V
INCD
> 2.5V
0 to 2A
0 to 2A, V
INGH
> 3.3V
1.2
2.5
1.8
3.3
5.5
5.5
V
V
V
V
V
V
BoarD photo
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DEMO MANUAL DC2311A
Quick start proceDure
The DC2311A is easy to set up to evaluate the performance
of the LTC3370. Refer to Figure 1 and Figure 2 for proper
measurement equipment setup and follow the evaluation
procedure below.
NOTE. When measuring the input or output voltage
ripple, care must be taken to avoid a long ground lead
on the oscilloscope probe. Measure the input or output
voltage ripple by touching the probe tip directly across
the V
IN
or V
OUT
and GND terminals. See Figure 2 for
proper scope probe technique.
1. Set the JP1 – JP4 jumpers on the DC2311A board to
the ON position.
2. Set the JP5 jumper on the DC2311A board to the
BURST position.
3. Set the JP6 jumper on the DC2311A board to the V
CC
position.
4. With power off, connect a 0V to 6V, 50mA power sup-
ply (PS5) to V
CC
input terminal and GND with a series
ammeter and a voltmeter as shown in Figure 1.
5. Turn on and set the PS5 to a desired input voltage
between 2.7V and 5.5V.
6. With a digital volt meter, measure the voltage on the
temp pin. This represents the die temperature,
(V
TEMP
– 45mV)/7mV = °C. 220mV = 25°C
7. With power off, connect 0V to 6V, 2A power supplies
to each input pair (PS1-PS4), V
INAB
, V
INC
/V
IND
, V
INE
/
V
INF
, V
ING
/V
INH
and GND with a series ammeter and
a voltmeter as shown in Figure 1. A single 0V to 6V,
10A supply can be used instead to supply all V
IN
inputs
and the V
CC
input simultaneously.
8. Turn on and set the PS1 input power supply to 5.0V
and observe that V
OUT1
regulates to 1.2V.
NOTE. Make sure that the input voltage does not exceed 6V.
9. With power off, connect a 0A to 2A load to V
OUT1
and
GND with a series ammeter and a voltmeter as shown
in Figure 1.
10. Slowly increase the load from 0A to 2A and observe the
output voltage. The output ripple may also be observed
using an oscilloscope with the probe connected as
shown in Figure 2.
11. Set Load1 to 100mA.
12. Repeat steps 8 to 11 for each output using their
respective power supplies and loads. Each output
voltage should regulate to the voltage indicated on
the silkscreen of the DC2311A.
13. Momentarily short V
OUT1
to ground with a clip lead and
observe that the PGOODALL LED, D1, on the demo
board illuminates. The LED shuts off when the short
is removed.
14. With Load1 set to 100mA, observe the burst mode
ripple on V
OUT1
.
15. Set the JP5 jumper on the DC2311A board to the
FORCED CONT position and observe the forced con-
tinuous mode ripple on V
OUT1
.
16. With an oscilloscope using two probes each set to
1V/Div vertical scale and 1µs/Div horizontal scale,
compare the phase between SWAB to SWCD, SWEF,
and then SWGH. Observe that the switch nodes are
90°, 270°, and 180° out of phase respectively with
SWAB.
17. Set the JP5 jumper on the DC2311A board to the PLL
position.
18. Set a pulse generator to output a 0V to 5V pulse at
2MHz, 50% Duty cycle and connect it to the PLL/MODE
terminal and GND.
19. Change the frequency of the pulse generator from
2MHz to 3MHz and observe how the frequency of
SWAB follows the pulse generator.
20. Set LOAD1 greater than 1.0A. With an oscilloscope
probe on SWAB, remove the pulse signal to the PLL/
MODE terminal and observe how the switch frequency
settles from 3MHz back to 2MHz.
21. Refer to the LTC3370 data sheet for more details on
how the LTC3370 operates.
22. When done, turn off all loads and power supplies.
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DEMO MANUAL DC2311A
moDifying the Dc2311a to other power configurations
The LTC3370 can be configured to one of eight different
power configurations as shown in Table 1. To reconfigure
the DC2311A to a different configuration some resistors
will need to be changed, traces will need to be shorted
together, and often traces will need to be cut. Follow the
steps below to modify the board to a desired configuration.
1. Choose the desired configuration from Table 1.
Table 1. Master Slave Program Combinations (Each Letter
Corresponds to a V
IN
and SW Pair)
PROGRAM
CODE
C3C2C1
000
001
010
011
100
101
110
111
BUCK 1
AB
ABC
ABC
ABCH
ABC
ABCD
ABCD
ABCD
BUCK 2
CD
D
D
D
DE
Not Used
Not Used
Not Used
BUCK 3
EF
EF
E
E
Not Used
EF
E
Not Used
BUCK 4
GH
GH
FGH
FG
FGH
GH
FGH
EFGH
Figure 3. C Bit Resistors and Optional Output
Capacitors for V
OUT1
and V
OUT4
2. Set the associated C bit pins high or low as per Table 1
by opening and shorting the appropriate resistors. C1,
C2, and C3 are set high by shorting R7, R11, and R14
respectively. C1, C2, and C3 are set low by shorting
R9, R13, and R16 respectively. The C bit resistors are
0603 resistors located on the bottom of the board as
shown in Figure 3.
3. The DC2311A is set up with the following power stage
switch nodes and V
IN
nodes connected together; A &
B, C & D, E & F, and G & H. Any configuration using
1A or 3A regulators will require one or more of the V
IN
and switch nodes to be separated. Refer to Table 1 to
determine which power stages are connected together
and separated. Cut the required V
IN
nodes by cutting
the V
IN
traces on the bottom of the board near the V
IN
terminals as shown in Figure 4.
Figure 4. Separate V
IN
Pairs by Cutting Traces at Terminals
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